8.36.1 Compression What Boost To Run?

[zebra]

If you can retard the timing 8degrees from MBT (Minimum best timing) and not loose any torque you have built a non dynamic engine. This maybe due to low compression pistons combined with larger duartion camshafts. The other problem with thicker head gaskets is that you reduce the squish clearance which has a huge effect on timing sensitivity.

You should be able to put a bit more boost into the engine to give you more cylinder fill but anything more than about 25psi with that turbo on an RB25 is pushing you outside the efficiency of that turbine. I would try that first and if the engine is still unsensitive with ignition timing changes then I would be putting a thinner head gasket in to raise your static and dynamic compression.

im thinking the same thing,

I had the same problem with my Rb25, i could pull 10deg of timing out of it and lose only 10rwkw,

I had 8.5:1 comp and standard cams so the issue will be worse with larger cams and less comp.

[17psi r33]

im thinking the same thing,

I had the same problem with my Rb25, i could pull 10deg of timing out of it and lose only 10rwkw,

I had 8.5:1 comp and standard cams so the issue will be worse with larger cams and less comp.

wow got a few replys so far, did raising the compression fix your problem? and as far as that turbo being maxed out i dont really think so it was able to push 1.9 bar all the way to red line when my wategate was playing up. there is another person on this form who said he achived 500plus hp with type turbo, ill squize this setup to it max befor ill pull the head off myself. im a fan of not paying work whops to do realativly easy work, so ill research the head gasket change while tuning this setup. the only problem with going a bigger turbo to is the type of manifold im using, as im sure i wont fit a much larger one ie 3540 on a low mount hks cast iron manifold.

[Adriano]

3582 im pretty sure fits on an hks low mount manifold. The guy who has 500hp, is that at the crank? The problem is the 1.9 bar, 5 psi of that is just making up for the low comp, and 1.9 bar doesnt mean it will make any more power than 1.6 bar

[The Mafia]

My Old Specs:

Stock Standard Motor with 100,000kms

WMI

GT3076, 0.63rear

18psi

98ron

Supporting mods

314rwkw (420rwhp)

20psi, made 430rwhp

720nm torque from 3000rpm in third, all the way to the limiter.

You need a new tuner, and more boost. I'd say about 25psi to equal a standard motor running 9:1 and 20psi of boost.

Oh, and throw that head gasket in the bin, and get a 1mm gasket and raise the compression.

Edited June 29, 2010 by The Mafia

[wolverine]

as im sure i wont fit a much larger one ie 3540 on a low mount hks cast iron manifold.

I have a GT3040 on my HKS low mount. You need to machine the engine mount a bit.

[17psi r33]

3582 im pretty sure fits on an hks low mount manifold. The guy who has 500hp, is that at the crank? The problem is the 1.9 bar, 5 psi of that is just making up for the low comp, and 1.9 bar doesnt mean it will make any more power than 1.6 bar

were did you find info on that turbo fitting that manifold? and ill search today for my claimed mistery man making 500hp with that turbo.

[17psi r33]

My Old Specs:

Stock Standard Motor with 100,000kms

WMI

GT3076, 0.63rear

18psi

98ron

Supporting mods

314rwkw (420rwhp)

20psi, made 430rwhp

720nm torque from 3000rpm in third, all the way to the limiter.

You need a new tuner, and more boost. I'd say about 25psi to equal a standard motor running 9:1 and 20psi of boost.

Oh, and throw that head gasket in the bin, and get a 1mm gasket and raise the compression.

yea im looking into changing the head gasket just finding out what i require to change it out. and also your not a mackay resident are you?

[Dale FZ1]

my motor was tuned at 20psi with a garret gt3076r im only at 70% injector duty...

its only making 380rwhp...

550cc injecrtor, watermethanol injected...

the tuner said he could back the timing off 8 deg retard and the peak power stayed the same

Points of interest from original post bolded, looking to clarify your situation and even the approach to tuning.

Are you running stock fuel pressure? Assuming so, then with injector duty cycle 70% then total fuel flow should support approx 380 hp @ the crank, not the wheels. Or has your tuner significantly leaned off the full load/high rpm fuelling to match W/M delivery? Might be worth reviewing any datalogs you may have acquired during the tune.

Another issue to consider is that if you are introducing a significant proportion of W/M then the std ignition system may not be coping that well. There may be a lack of grunt in the spark department - time for a CDI? Have you discussed with your tuner how aggressive the W/M delivery is? I'd be thinking the lack of response to ignition timing could be that the total tune (fuel, W/M, spark) and mechanical spec gives very high knock resistance but there is a factor holding it back a touch. I'd lean towards spark energy rather than static C.R.

Assuming your inlet and exhaust pipework is all decent free flowing ie. you're not stuffing 20psi boost in against a large amount of back pressure - then you'd probably expect to achieve up to 430rwhp +/- 10hp. That turbo probably won't push much/any greater air mass, but with W/M the engine should be nearly bomb proof. 500rwhp is a lot to chase from an RB25, you might send Fineline a PM for his views.

Do you have a dyno sheet to help with this thread?

[zebra]

wow got a few replys so far, did raising the compression fix your problem? and as far as that turbo being maxed out i dont really think so it was able to push 1.9 bar all the way to red line when my wategate was playing up. there is another person on this form who said he achived 500plus hp with type turbo, ill squize this setup to it max befor ill pull the head off myself. im a fan of not paying work whops to do realativly easy work, so ill research the head gasket change while tuning this setup. the only problem with going a bigger turbo to is the type of manifold im using, as im sure i wont fit a much larger one ie 3540 on a low mount hks cast iron manifold.

I cant say if raising the comp fixed my issue, the motor went bang and it hasnt been back on a dyno with 9:1 comp

[17psi r33]

Points of interest from original post bolded, looking to clarify your situation and even the approach to tuning.

Are you running stock fuel pressure? Assuming so, then with injector duty cycle 70% then total fuel flow should support approx 380 hp @ the crank, not the wheels. Or has your tuner significantly leaned off the full load/high rpm fuelling to match W/M delivery? Might be worth reviewing any datalogs you may have acquired during the tune.

Another issue to consider is that if you are introducing a significant proportion of W/M then the std ignition system may not be coping that well. There may be a lack of grunt in the spark department - time for a CDI? Have you discussed with your tuner how aggressive the W/M delivery is? I'd be thinking the lack of response to ignition timing could be that the total tune (fuel, W/M, spark) and mechanical spec gives very high knock resistance but there is a factor holding it back a touch. I'd lean towards spark energy rather than static C.R.

Assuming your inlet and exhaust pipework is all decent free flowing ie. you're not stuffing 20psi boost in against a large amount of back pressure - then you'd probably expect to achieve up to 430rwhp +/- 10hp. That turbo probably won't push much/any greater air mass, but with W/M the engine should be nearly bomb proof. 500rwhp is a lot to chase from an RB25, you might send Fineline a PM for his views.

Do you have a dyno sheet to help with this thread?

no im not running standard fuel pressure i have a 044 intank and runing around 65psi from memory on load and around 30 psi at idle and no its 380 at wheel hp, wmi is a 175c injector so not pumping heaps in, and spark problem most likely not as i have upgraded spark plugs and split fire coils packs. just hit up tuner today to send dyno sheet so some time today ill post it.

[Dale FZ1]

That's equating to ~ 8% water:fuel at the cited injector duty cycle which isn't heaps but is heading in the right direction.

Ask your tuner for overlay of AFR. Be nice to see that.

I'm not 100% convinced that even brand new coil packs (Splitfire or any other brand to suit RB) have enough spark energy to deal with water injection, hence the comments about CDI.

What is your tuner's view?

[17psi r33]

That's equating to ~ 8% water:fuel at the cited injector duty cycle which isn't heaps but is heading in the right direction.

Ask your tuner for overlay of AFR. Be nice to see that.

I'm not 100% convinced that even brand new coil packs (Splitfire or any other brand to suit RB) have enough spark energy to deal with water injection, hence the comments about CDI.

What is your tuner's view?

ill have to ask him what his view is on the ignition system with wmi on rb25det, nearly all cars he tunes her in mackay is advised to have one added as it helps with the heat of up north and also a safety precausion, and ive asked for my dyno sheet that shows Hp bosst tourqe and afr so you get a clear idea of where the tune is at.

[The Mafia]

Dale has got the right idea.

I am in mackay, and I do a lot of tuning. Who is doing your tuning? There are a lot of people in mackay that you need to stay away from.

I have split fires, and they have never missed a beat.

http://www.youtube.com/watch?v=v3A_6gF1McY

Edited June 30, 2010 by The Mafia

[17psi r33]

Dale has got the right idea.

I am in mackay, and I do a lot of tuning. Who is doing your tuning? There are a lot of people in mackay that you need to stay away from.

I have split fires, and they have never missed a beat.

http://www.youtube.com/watch?v=v3A_6gF1McY

yea i noticed after you replyed in the other disscusion that your a local, ha ha. adrenalin performance has been tuning my car since i moved up here, it was CnJ motorsports in brisbane first off, what ecu are you running?

[T04GTR]

perhaps if it was 8.37:1,or 8.35:1 your issues will go away.....

if the engine was put together "corectly" and tuned "properly" you could just keep putting boost into it till it stops making power.

which will be injectors,spark breakdown,turbine back pressure, valve springs. generaly in that order. not your comp ratio.

back in the day, "group a" ran 7:1 nowdays 9.5-10:1 is the go. fuels and ecu's are alot better today. all for about the same power.

with spark, it will missfire or not missfire. changing coils will not solve the problem. (unles they leak) alot of the jap drag cars still use stock coils.

[17psi r33]

perhaps if it was 8.37:1,or 8.35:1 your issues will go away.....

if the engine was put together "corectly" and tuned "properly" you could just keep putting boost into it till it stops making power.

which will be injectors,spark breakdown,turbine back pressure, valve springs. generaly in that order. not your comp ratio.

back in the day, "group a" ran 7:1 nowdays 9.5-10:1 is the go. fuels and ecu's are alot better today. all for about the same power.

with spark, it will missfire or not missfire. changing coils will not solve the problem. (unles they leak) alot of the jap drag cars still use stock coils.

engine was definatly assembled correctly as i was there to do it, but the annoying part is the tuner keeps limiting the boost to 20psi and keeps dicken around at that level trying to get better power from 20psi as he thinks it should be making more power than that, where as i keep saying just wind the bugger up!

[BezerkR32]

dont ususally post in this section as there are already so many experts, but noticed there is no mention of valve spring upgrade in your build, this could be why your tuner is limiting boost around 20psi as rb25 standard valve springs are about maxed out at high rpm and that boost.

standard rb25 with gt35/40 will make 300kw atw on 20 psi. so you might be looking for a bigger compressor to flow more at that pressure to make up the difference.

disregard the valve spring comment if you have upgraded them.

engine was definatly assembled correctly as i was there to do it, but the annoying part is the tuner keeps limiting the boost to 20psi and keeps dicken around at that level trying to get better power from 20psi as he thinks it should be making more power than that, where as i keep saying just wind the bugger up!

[17psi r33]

dont ususally post in this section as there are already so many experts, but noticed there is no mention of valve spring upgrade in your build, this could be why your tuner is limiting boost around 20psi as rb25 standard valve springs are about maxed out at high rpm and that boost.

standard rb25 with gt35/40 will make 300kw atw on 20 psi. so you might be looking for a bigger compressor to flow more at that pressure to make up the difference.

disregard the valve spring comment if you have upgraded them.

unfortunatly no valve spring upgrade done, thought about it at the time of build but was informed they are relativly good from the start, but if i end up pulling the head again which is on the cards then a valve and cam upgrade are on the cards, bullit cams and somewhere around the 282deg area will be where im looking. there are a few other cars on this site making big power with standard motors and huge turbos so cant see why i really need to change valve springs.

[discopotato03]

I think people need to have a base line and have a look at what these cars/engines did out of the box .

I'll assume a standard S2 GTS25T makes 185Kw which equates to 247 Hp or 99 Hp per liter . If you want 500 Hp from that engine the numbers crunch to 200 Hp/L so 100% increase .

Given the opportunity generally cubic inches make the easiest horses so factor 3 liters into the equation , 500 divide 3 equals 167 Hp/L . They make more torque because they are a larger air pump , ~ 20% larger .

They'll spool a larger more capable turbocharger earlier than an RB25 whilst making more torque down low .

You would be asking a lot from a real GT3076R to pump 50+ pounds of airflow and using the largest available housings would be the way to do it efficiently . On an RB30 a GT3582R would do it easily if everything was done right .

Think hard for a sec what Mr Mafia said about his torque number - 720 Nm from 3000 to maximum revs .

I wonder how many RB25's wearing big turbos can do the same or better from 3000 .

Take it to the grave , TORQUE is everything while Hp/Kw is a fancy Mores law way of impressing Joe average with a healthy looking number . If manufacturers were being truly helpful they would rate their engines on torque numbers rather than a torque number multiplied by engine revs . Turbo diesels are a good example to look at , advertised as making SFA Kw's but the torque numbers can be fantastic - compared to a same capacity petrol engine .

The other thing is that tractive effort is critical when you start getting good torque numbers , all the torque in the world is useless if it goes to the dogs with wheel spin . A lot of money gets spent making power that will likely never be useful without very capable tyres/suspension on a real good surface in dry weather . And even then I'd reckon its going to be tail happy driven hard .

Can reduce the timing 8 degrees (sounds like across the board) , and the torque peak doesn't change ? Something really wrong with the tuning method there .

I really had hoped we'd grown beyond the stage of reducing static CRs by using thicker head gaskets - particularly in an engine that's been opened up and better pistons fitted . THIS IS DARK AGES GARBAGE !

The dinosaur theory was that increasing the volume above the cylinders swept volume reduced the CR which lowered the cylinder pressure/temperature before the forced induction artificially boosted it .

Trouble is that the further the piston crowns are from the heads quench pads the worse the chamber shape becomes and this often LOWERS an engines detonation threshold purely because the quench areas don't work as well .

Pent roof combustion chambers and four valves per cylinder were designed to give you a lot of valve (breathing) area in a compact combustion chamber and part of keeping the chamber area small was having those flat "D" shaped sections beyond each pair of valves . Jacking the head up on a thicker gasket increases the large flat washer area above the flat outer area of the piston crowns so it can now have a greater volume for end gasses to hide in and auto ignite before the spark initiated flame front reaches them . Result - rattle rattle bang bang $$$$$$$$$$$$$$$$$$$$$$$$$$$ .

The correct method is to have the right volume in the pistons dish to set the static CR which then leaves minimul volume between the piston crowns and the head face , smaller volume of end gasses , air and fuel , less to detonate .

For its day the old Cosworth BDA (Belt Drive A Series) had very good chambers but the narrow valve angles are hard to make in a head that's not very tall - like most twin cam production heads are for engine bay packaging reasons .

Another epic I know .

Bottom line is that traction is the limiting factor and torque beyond tractive effort is pointless .

The other one is that torque wins races and horsepower sells cars , its as relevant today as is was a lifetime ago because the physics haven't changed .

AWD is the only practical way to have high tractive effort in an un tubbed car . Sad but true .

The good news is that E85 at the bowser is coming so hopefully there will be a cheaper way around octane limited ULP and we will be able to make good torque with less extreme states of engine tune .

A .

[17psi r33]

I think people need to have a base line and have a look at what these cars/engines did out of the box .

I'll assume a standard S2 GTS25T makes 185Kw which equates to 247 Hp or 99 Hp per liter . If you want 500 Hp from that engine the numbers crunch to 200 Hp/L so 100% increase .

Given the opportunity generally cubic inches make the easiest horses so factor 3 liters into the equation , 500 divide 3 equals 167 Hp/L . They make more torque because they are a larger air pump , ~ 20% larger .

They'll spool a larger more capable turbocharger earlier than an RB25 whilst making more torque down low .

You would be asking a lot from a real GT3076R to pump 50+ pounds of airflow and using the largest available housings would be the way to do it efficiently . On an RB30 a GT3582R would do it easily if everything was done right .

Think hard for a sec what Mr Mafia said about his torque number - 720 Nm from 3000 to maximum revs .

I wonder how many RB25's wearing big turbos can do the same or better from 3000 .

Take it to the grave , TORQUE is everything while Hp/Kw is a fancy Mores law way of impressing Joe average with a healthy looking number . If manufacturers were being truly helpful they would rate their engines on torque numbers rather than a torque number multiplied by engine revs . Turbo diesels are a good example to look at , advertised as making SFA Kw's but the torque numbers can be fantastic - compared to a same capacity petrol engine .

The other thing is that tractive effort is critical when you start getting good torque numbers , all the torque in the world is useless if it goes to the dogs with wheel spin . A lot of money gets spent making power that will likely never be useful without very capable tyres/suspension on a real good surface in dry weather . And even then I'd reckon its going to be tail happy driven hard .

Can reduce the timing 8 degrees (sounds like across the board) , and the torque peak doesn't change ? Something really wrong with the tuning method there .

I really had hoped we'd grown beyond the stage of reducing static CRs by using thicker head gaskets - particularly in an engine that's been opened up and better pistons fitted . THIS IS DARK AGES GARBAGE !

The dinosaur theory was that increasing the volume above the cylinders swept volume reduced the CR which lowered the cylinder pressure/temperature before the forced induction artificially boosted it .

Trouble is that the further the piston crowns are from the heads quench pads the worse the chamber shape becomes and this often LOWERS an engines detonation threshold purely because the quench areas don't work as well .

Pent roof combustion chambers and four valves per cylinder were designed to give you a lot of valve (breathing) area in a compact combustion chamber and part of keeping the chamber area small was having those flat "D" shaped sections beyond each pair of valves . Jacking the head up on a thicker gasket increases the large flat washer area above the flat outer area of the piston crowns so it can now have a greater volume for end gasses to hide in and auto ignite before the spark initiated flame front reaches them . Result - rattle rattle bang bang $$$$$$$$$$$$$$$$$$$$$$$$$$$ .

The correct method is to have the right volume in the pistons dish to set the static CR which then leaves minimul volume between the piston crowns and the head face , smaller volume of end gasses , air and fuel , less to detonate .

For its day the old Cosworth BDA (Belt Drive A Series) had very good chambers but the narrow valve angles are hard to make in a head that's not very tall - like most twin cam production heads are for engine bay packaging reasons .

Another epic I know .

Bottom line is that traction is the limiting factor and torque beyond tractive effort is pointless .

The other one is that torque wins races and horsepower sells cars , its as relevant today as is was a lifetime ago because the physics haven't changed .

AWD is the only practical way to have high tractive effort in an un tubbed car . Sad but true .

The good news is that E85 at the bowser is coming so hopefully there will be a cheaper way around octane limited ULP and we will be able to make good torque with less extreme states of engine tune .

A .

yes your right about a few things in there, as it is i have great suspension setup and not the best tyers but still traction will always be a problem for any rwd car, and also might i add, and no this is not another topic starter for the world. if 4wd is so so so great why are top fuelers rwd? any way i dont think chasing a figure is so bad ie 500 hp, your right it is for show and tell:) and the age old saying of tourqe makes fast cars hp sells cars is so true. but i built it with a figure in mind that i think is achivable so ill get as close as i can to it. and i am catching up with mafia some time in the next week or to to see what dyno he got his results on, as mine made similar tourqe but on a chassie dyno, but was told thats not a real result as it wont be a realistic torque result. dont know why thought. oh and sorry its not made 720nm it was 750flb. but as far as the current set up for my compression im looking into going back to around the 9.0.1 if i cant get the hp to where i want, ill try first to see what i can do befor spending money again. maybe its my tuners skills not sure yet. waiting for MY DAM DYNO SHEET!!!!!!!!!!!!!!!!